Find tail probability for a t-distribution using EXCEL

[Pages:3]Find tail probability for a t-distribution using EXCEL

Tail probability is the value that is often used for finding p-value. The following example is to find the left tail probability or cumulative probability using EXCEL for a t-score of 2.64 in a tdistribution with a degree of freedom 14. To do that, click on any cell in the EXCEL worksheet and type =T.DIST(2.64, 14, TRUE). T.DIST is an EXCEL function. To use an EXCEL function, we need to start with an "=" sign and then type the function. The first parameter in the T.DIST function is the t-score, the second parameter to enter is the degree of freedom, and if you enter "TRUE" for the last parameter, this function will show you the left tail probability or the cumulative probability at 2.64 in a t-distribution with d.f. of 14. It is 0.9902979. To get the right tail probability, one would need to subtract 0.9902979 from 1.

Find tail probability for a Normal distribution using EXCEL

Similar to the previous example, enter "=NORM.S.DIST(2.64, TRUE)" in a cell in EXCEL worksheet gives you the left tail probability from a standard normal (z) score of 2.64. It is 0.9958547.

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Find tail probability for a t-distribution using R Commander

To find the cumulative probability at a t-score of 2.64 from a t-distribution with d.f. of 14 using R Commander, you can select the following path: Distributions / Continuous distribution / t distribution / t probabilities

Enter the t-score and the d.f. and have the Lower tail bullet checked and click OK. You should be able to see the probability 0.9902979 in the R Commander Output Window. You may check the Upper tail bullet checked if you wish to find the right tail probability. It would be 1 minus the left tail probability.

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Find tail probability in a standard normal distribution using R Commander

To find the cumulative probability at a z-score of 2.64 from a standard normal (z) distribution using R Commander, you can select the following path: Distributions / Continuous distribution / Normal distribution / Normal probabilities

Enter the z-score 2.64. For standard normal distribution, the mean is 0 and the standard deviation is 1. And, have the Lower tail bullet checked and click OK. You should be able to see the left tail probability 0.9958547 in the R Commander Output Window. You may check the Upper tail bullet checked if you wish to find the right tail probability. It would be 1 minus the left tail probability.

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